Scents that make you trackable, indoors and out. Nanocrystals that stick to your body, and light up on night-vision goggles. Miniradar that maps your location on Google Earth.

You can run, but you'll learn it's hard to hide from a new range of military tech.

The Defense Department calls it "tagging, tracking and locating," or TTL, this business of finding and following high-value targets on the battlefield. Ever since SEAL Team 6 took out Osama bin Laden, we've learned a lot about the technology used by special operators to find and reach their targets, from stealth helicopters to biometric identification devices. TTL gear, though, ranks among the spookiest Special Operations' extremely spooky arsenal.

Al-Qaida says it found spies using infrared beacons to call in drone strikes in Pakistan. A Pakistani Taliban commander claims the United States puts tracking "chips" in cellphones, in order to train Hellfire missiles on militants. But these aren't the only technologies that can to secretly track people.

With one technology, trackers might not even need to see you to get a fix on your location. Like bloodhounds on the hunt, they can smell their way to you. Tracer Detection Technology Corp. marks targets with a paraffin wax crayon, filled with a perfluorocarbon, a thermally-stable compound used in everything from refrigerators to cosmetics. The perfluorocarbon's vapor can then be tracked with sensors, such as a gas chromatograph. The smell lingers for hours. Think locking yourself in a room with the windows closed or removing the tag will help? Too bad, you still reek. According to a research report submitted to the Justice Department (.pdf), the perfluorocarbon tracers can "permeate closed doors and windows, containers and luggage," and even give you away for a while after a tagged item is removed.

Over the years, the company has received a number of research contracts from the Navy. But Tracer president Jay Fraser won't say much about how those projects have gone. "Tracer is developing a unique TTL capability that will make it very difficult for enemy and criminal enterprises to operate," he e-mails Danger Room. "The nature of our current and pending customers makes it hard for us to answer the rest of your questions."

Now a second tracer: Imagine walking up to a target and patting him on the back with a clear liquid on your hand. He might never notice it, but you'd be able to see - and follow - him from a distance using night vision goggles. Oregon-based Voxtel makes a product, "NightMarks," that can do just that. NightMarks are tiny nanocrystal quantum dots that can be hidden in clear liquids and seen only through a sensor like night-vision goggles.

How do these tiny dots work? "You can change the optical properties of materials by making them small on the order of a nanometer in size," Voxtel CEO George Williams tells Danger Room. "When they get down to that size, they have quantum-confinement effects that cause their absorption and emission properties - the light they absorb, the light they put out - to change," he says. "And so using that, you can make all sorts of spectral barcodes that allow you to identify it and track."

Williams is tight-lipped about Voxtel's relationship with the Defense Department and the military applications of its technology. However, a quick look at one 2008 Voxtel contract with the Navy indicates that the Department already understands how useful the technology can be for tracking targets. The contract asks for "covert microtaggants composed of nanocrystals" visible through sensors like night-vision goggles to "enable war fighters the ability to track entities buried in urban clutter."

Another company has proposed a somewhat counterintuitive solution for military tagging: making sure its signal decays. You might think that being able to see a taggant signal for as long as possible is always a good thing, but according to a briefing (.pdf) from TIAX LLC, it can actually be a problem.

Leftover taggants that last for long periods of time can apparently clutter up an area with signals, and the mess can hinder a tracker's ability to distinguish between the subjects of new and old tags. If they're still advertising their presence long after usefulness, opponents might also be able to find and reverse-engineer the material. To get around the problem, the briefing mentions that TIAX is working on "customizable degradable taggants" - exact composition unspecified - that will lose their signal over time.

Other technologies are useful in defensive tracking, such as for perimeter security on small firebases. SpotterRF, makes a small radar-sensor system, the SpotterRF M600, that's about the size of a small netbook computer and can conveniently point out humans creeping up on your position on Google Earth. The M600 uses radio waves in the X band that can detect walkers up to 1,000 meters [0.62 miles] and vehicles as far away as 1,500 meters. It integrates with Google Earth by using its own built-in GPS to fix the device's position and overlay tracked targets onto the mapping service.

The effect, a company rep e-mails, is "like being able to stick a GPS tracking device on someone without having to come anywhere near the person or vehicle." It's yet another way to hunt someone down who might not want to be hunted.

Above:

Micro Radio Transmitter

Oak Ridge National Laboratories developed this micro-miniature radio frequency transmitter (above). It's smaller than a dime, and has a range of three kilometers [1.9 miles].

Quantum-Dot Tagging

This picture from a Sandia National Labs report shows quantum dots - crystals that change their optical properties, depending on their size. These dots are made of cadmium selenide, illuminated on a paper towel. Oregon-based Voxtel makes nanocrystal quantum dots that can be hidden in clear liquids and seen through night-vision goggles.

Image: Sandia National Laboratories

Infrared-Flash Tagging

In June 2009, al-Qaida released an electronic book, The Ruling Concerning Muslim Spies, which claimed to publish photos of some of the devices Pakistani "spies" used to guide American drone strikes. The pictures appear to show infrared beacons, powered by a 9-volt battery.

Image courtesy Nine Eleven Finding Answers Foundation

Radar-Responsive Tag

Sandia National Laboratories has carried out development on these radar-responsive tags, which are like a long-range version of the ubiquitous stick-on RFID tags used to mark items in shops. The radar-responsive tag stays asleep until it is awakened by a radar pulse. The tags in Walmart have a range of a couple of meters, Sandia's tags can light up and locate themselves from 12 miles away.

Image: Sandia National Laboratories

SpotterRF Tag

The M600 made by SpotterRF is a compact radar system useful for tracking humans and vehicles on small firebases or in perimeter security. The five-pound system can detect humans walkers out to 1,000 meters [0.62 miles] and vehicles up to 1,500 meters, and plot their positions on Google Earth.

Image: SpotterRF

Human Thermal Fingerprint

In its 2007 briefing
, U.S. Special Operations Command also describes its goal of identifying targets by their body heat or "human thermal fingerprint" from a long distance away.

Image: Special Operations Command

Chemical Light-Stick Tag

Another photo from al-Qaida's The Ruling Concerning Muslim Spies
: It appears to be chemical light sticks - again, used to signal to the drones where to strike.